1. Field of the invention
The present invention relates to engines and more particularly to a rocker arm for relatively large oil well pumping engines.
In producing oil fields pumping units are employed for operating down hole pumps to lift the oil to the surface of the earth. In some of these oil fields, commonly known as shallow fields, a single engine, such as a No. 346 or No. 503 Fairbanks, Morse and Co. engine, is centrally located with respect to a number of the wells and horizontally rotates a control wheel of relatively large diameter for reciprocating a plurality of eccentrically connected lift strings separately connected with like a plurality of pumping jacks at respective well locations. These lift strings are usually formed from sucker-like rod material and one such engine is capable of pumping several oil wells. This engine generally has its single cylinder horizontallly disposed and its cylinder head is equipped with spring urged intake and exhaust valves, the intake valve being opened by reduced pressure in the engine cylinder and the exhaust valve being opened by a cam operated push rod moving a rocker arm in sequence with the engine timing.
2. Description of the prior art
Respective end portions of the exhaust valve rocker arm in the above described engines have usually been hardened or at least case hardened to prolong their life and reduce the wear thereto caused by continuous contact with the exhaust valve stem and the push rod. The resulting wear necessitates replacement of the rocker arm as well as some arrangement for adjusting the magnitude of rocking movement of the rocker arm and insuring full opening and closing of the valve. This has been accomplished to some extent by providing a screw at the push rod end of the rocker arm which may be threadedly moved axially toward and away from the push rod and held in place by a lock nut.
A friction reducing roller has also been installed on the opposite end of the rocker arm for contact with the valve stem. While this arrangement has been generally satisfactory it does not provide accurate aligned contact of the roller with the valve stem axis resulting in a lateral force on the valve stem tending to wear the valve guide and resultant necessary repairs to the engine and a loss of oil production during such down time.
This invention provides a means for obtaining accurate alignment of the rocker arm roller with the exhaust valve stem.